The present invention relates to a method for preparing polyacrylonitrile (PAN)-based activated carbon fabrics for providing adsorption and, in particular, to a method for preparing PAN-based activated carbon fabrics from a PAN-based oxidized fabric.
In U.S. Pat. No. 4,362,646 issued to Ikegami et al, it is disclosed that PAN-based activated carbon fibers are superior to pitch-based, cellulose-based and phenol resin-based activated carbon fibers in their mechanical strength and their ability to aborb due to the nitrogen atoms contained therein.
The inventors of the present invention, in Journal of Material Science Letters (Vol. 1, pp. 6-8, 1992), disclose a process for preparing PAN-based activated carbon fibers. The process includes first preparing oxidized carbon fibers by shrinking polyacrylonitrile fiber bundles in an oxidizing process, followed by activating the oxidized carbon fibers in a carbon dioxide atmosphere at a temperature of 900.degree. C. The PAN-based activated carbon fibers thus prepared are found to have moderate tensile strength (above 0.46 Gpa), and excellent adsorbing ability to absorb dyestuffs dissolved in wastewater.
In addition, in Carbon (Vol. 30, pp. 647-655, 1992), the inventors also disclose a process for the preparation of PAN-based carbon fibers in which polyacrylonitrile fiber bundles are oxidized, and then activated at 880.degree. C. by using a carbon dioxide gas as an activating gas. Thus produced activated carbon fibers have a BET surface area higher than 500 m.sup.2 /g and a tensile strength higher than 0.5 Gpa.
PAN-based activated fibers have superior adsorbing ability and mechanical strength. It is desirable to weave PAN-based activated fibers into fabrics used as adsorption material for waste gas and waste water. However, if PAN-based activated carbon fibers are to be woven into a fabric, the following complicated process is required: PAN-based fiber bundles.fwdarw.oxidization.fwdarw.activation.fwdarw.activated carbon fiber bundles.fwdarw.carding.fwdarw.spinning.fwdarw.activated carbon yarn.fwdarw.weaving.fwdarw.activated carbon fabrics. However, as activated carbon fibers are fragile, permitting an elongation of less than 1.5%, they are easily broken in the carding, spinning and weaving process, and therefore are not suitable for being woven into fabrics, but only suitable for forming of fiber bundles, non-woven fabrics, papers or felts.
In Japan Laid-open Patent No. 60-231834, a process for preparing activated carbon fabrics by using fabrics woven from a first fiber including a cellulose or phenol resin fiber, and a second fiber is disclosed. The first fiber can be activated, thereby allowing the resulting activated carbon fabrics to have adsorption. However, as the mechanical strength of first fibers will, during their activation process, degrade, the resulting products display poor mechanical strength.